Rotary presses for the production of tablets and similar pellets have upper and lower punches, which work together with die holes in a die plate in order to process filled-in powder into pellets. The molds with which the punches work are called dies and are fastened in holes of the die plate as separate sleeve-like inserts. However, it is also known to combine the die plate from segments and to produce the mold holes directly in the segments. (Although dies are not used for these types of segments, the plate, which is comprised of the segments, is still called a die plate.) The use of segmented die plates has the advantage that in the case of a change in the mold of the pellet the removal of the dies and the installation of new dies can be omitted. Moreover, the dies require a relatively large amount of space so that they restrict the number of mold holes on a specified reference circle. The number of mold holes in a die plate without die inserts is naturally larger.
Press punches of the named type have a punch head and a shaft. The punch head has a mirror surface on the top side, which works together with compression rollers in the rotary press. The diameter of the mirror surface determines the pressure hold time of the press punches, i.e. in the case of a given speed the time when the press punches work together with the powder to be pressed. The press punch heads also have a cylinder surface, and a rounded transition is arranged between it and the mirror surface, wherein the transition has a relatively large radius in order to let them first come into gradual effect when the compression rollers are lowered. On the bottom side, the punch heads transition into the shaft in a mostly conical section.
The mass of the punch of a rotary press and the associated inertia are a limiting factor for the machine speed and are also significant for the wear of punch heads and curves working together with them. Moreover, an unfavorable interaction results between the compression roller and the punch head through uneven transition of the compression roller from one punch head to the next. This causes considerable noise emission and wear on the punch and compression roller.
The geometric design and dimension of punch heads for rotary presses are standardized (DIN ISO 18084:2006-09). The diameter of the head, which is determined by the cylinder surface, is then either 25.27 or 31.6 mm, the diameter of the mirror surface is 9.6 or 16 mm, the diameter of the shaft is 19 or 25.35 mm and the height of the head is 8.15 mm.
The object of the invention is to create a punch for a rotary press, in which a smaller size is achieved, thus enabling a smaller separation distance of the punches. The noise emission can also be reduced.